Turn count decoding for multi-turn sensors

ABSTRACT

Aspects of the present disclosure relate to decoding the output of a multi-turn magnetic sensor using a successive approximation technique to detect a number of turns of a magnetic target. A decoder circuit can decode a turn count of the multi-turn magnetic sensor by obtaining measurements at nodes that are determined from values of previous measurements.

RELATED APPLICATION

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR § 1.57.This application is a divisional of U.S. application Ser. No.15/936,223, filed Mar. 26, 2018 and titled “TURN COUNT DECODING FORMULTI-TURN SENSORS,” the disclosure of which is hereby incorporated byreference in its entirety herein.

FIELD OF DISCLOSURE

The disclosed technology relates to multi-turn magnetic sensors.

BACKGROUND

A magnetic multi-turn sensor can track how many times an object thatincludes or is coupled to a magnetic target has been turned. An exampleof a magnetic multi-turn sensor includes a giant magnetoresistance (GMR)sensor.

Magnetoresistance can occur in thin film structures when twoferromagnetic layers are separated by a relatively thin non-magneticfilm. When two magnetic layers are parallel, resistance can drop to aminimal value. As the magnetic layers are turned so they are no longerin parallel alignment, electrical resistance can increase. Magneticsensors can include GMR resistors made with alternating ferromagneticalloy layers and non-magnetic layers. The resistance of the GMR resistorcan be sensitive to and varies with changes in an applied magneticfield. Wheatstone bridges using GMR resistors can be patterned on asemiconductor chip to detect the angular and linear motion of a magnet.

SUMMARY OF THE DISCLOSURE

One aspect of this disclosure includes a system for decoding a turncount of a multi-turn magnetic sensor, the system comprising: amulti-turn magnetic sensor comprising a magnetoresistive track, and adecoder circuit coupled to nodes of the magnetoresistive track. Thedecoder circuit can be configured to: detect a first pair of signalsfrom a first pair of the nodes, select a second pair of the nodes basedon values of the signals from the first pair of the nodes, detect asecond pair of signals from the second pair of the nodes, and determinea turn count of the multi-turn sensor based at least in part on thefirst pair of signals and the second pair of signals.

The system for decoding the turn count of the multi-turn sensor can haveone, all, or any combination of the following: the turn count canrepresent a number of half-turns; the decoder circuit is configured toselect the second pair of the nodes based on whether the first pair ofsignals are both within a predefined range; the magnetoresistive trackis laid out in a shape of a spiral, and the decoder circuit is coupledto nodes on opposite sides of a line that extends through a center ofthe spiral; the first pair of signals are voltages from half-bridgecircuits of the multi-turn magnetic sensor; a first bit representing theturn count is decoded based on values of the first pair of signals; thedecoder circuit is configured to determine a most significant bitrepresenting the turn count prior to determining other bits representingthe turn count; the decoder system is configured to determine the turncount based on measuring signals from up to and including 2^(i)different nodes of the magnetoresistive track, wherein a maximum turncount of the multi-turn magnetic sensor is less than or equal to 2^(i),and i is a smallest integer such that 2^(i) is greater than or equal tothe maximum turn count; or wherein the decoder circuit includes amultiplexer configured to select a node from among the nodes of themagnetoresistive track, an analog-to-digital converter configured togenerate a digital representation of a signal from the node, and adecoder logic circuit configured to determine the turn count based atleast in part on the digital representation of the signal from the node.

Another aspect of this disclosure includes a decoder circuit fordecoding a state of a multi-turn magnetic sensor using successiveapproximation, the decoder circuit comprising circuitry configured tocouple to nodes of a multi-turn magnetic sensor, measure pairs ofsignals from the at least some of the nodes selected using a successiveapproximation readout technique, and determine a turn count based atleast in part on the measured pairs of signals.

The decoder circuit can have one, all, or any combination of thefollowing: the successive approximation readout technique comprisesdetecting a first pair of signals from a first pair of the nodes,selecting a second pair of the nodes based on values of the signals fromthe first pair of the nodes, and detecting a second pair of signals fromthe second pair of the nodes; the first pair of signals are voltagesignals from half-bridge circuits of the multi-turn magnetic sensor; amost significant bit representing the turn count is decoded based onvalues of the first pair of signals; or the decoder circuit isconfigured to determine the turn count to a half turn resolution.

Another aspect of this disclosure includes a method of decoding a turncount of a multi-turn magnetic sensor, the method comprising:determining a pair of signals for a pair of locations of the multi-turnmagnetic sensor; selecting a second pair of locations of the multi-turnmagnetic sensor based at least in part on the values of the pair ofsignals; determining a second pair of signals for the second pair oflocations; and decoding the turn count based at least in part on valuesof the first pair of signals and the second pair of signals.

The method can include one, all, or any combination of: the second pairof the nodes is selected based on whether the first pair of signals areboth within a predefined range; a first bit representing the turn countis decoded based on values of the first pair of signals; a mostsignificant bit representing the turn count is decoded prior todetermining other bits representing the turn count; the first pair ofsignals are voltages from half-bridge circuits of the multi-turnmagnetic sensor, and the turn count is a half turns count; or themulti-turn magnetic sensor includes a magnetoresistive track laid out ina shape of a spiral, and the pair of locations are on opposite sides ofa line that extends through a center of the spiral.

For purposes of summarizing the disclosure, certain aspects, advantages,and novel features have been described herein. It is to be understoodthat not necessarily all such aspects, advantages, or features areachieved in accordance with any particular embodiment. Thus, the variousembodiments may include or optimizes one or more aspects, advantages, orfeatures as taught herein without necessarily achieving other aspects,advantages, or features as taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings and the associated description herein are provided toillustrate specific embodiments and are not intended to be limiting.

FIG. 1 is a schematic block diagram of a magnetic multi-turn anglesensor system that includes a multi-turn sensor and an angle sensoraccording to an embodiment.

FIG. 2 shows an example magnetic strip layout representation of amulti-turn sensor with a corresponding circuit schematic representationaccording to an embodiment.

FIG. 3 shows an example multi-turn sensor with an example readoutstructure according to an embodiment.

FIG. 4 shows an example circuit for decoding a turn count of themulti-turn sensor of FIG. 3 according to an embodiment.

FIG. 5 shows a flow diagram of an example process for decoding halfturns from outputs of a multi-turn sensor using a successiveapproximation readout technique according to an embodiment.

FIG. 6 shows a flow diagram of an example process for decoding halfturns from outputs of a multi-turn sensor using a successiveapproximation readout technique according to an embodiment.

FIG. 7 shows example voltage outputs from various nodes of a multi-turnsensor FIG. 3.

FIG. 8A is a schematic block diagram of a magnetic angle sensor systemthat includes a multi-turn sensor, angle sensor, and a processoraccording to an embodiment.

FIG. 8B is a schematic block diagram of a magnetic angle sensor systemthat includes a multi-turn sensor, angle sensor, and a processoraccording to another embodiment.

FIG. 8C is a schematic block diagram of a magnetic angle sensor systemthat includes a multi-turn sensor, angle sensor, and a processoraccording to another embodiment.

DETAILED DESCRIPTION

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings. The headings are provided for convenience only and do notnecessarily affect the scope or meaning of the claims.

Aspects of this disclosure relate to efficiently decoding a turn countof a multi-turn magnetic sensor. A turn count can be represented by ahalf turn count (HTC). Successive approximation techniques can be usedto decode a turn count of a multi-turn magnetic sensor. Such successiveapproximation techniques can efficiently determine points on amulti-turn sensor to read to decode the turn count. Outputs from amulti-turn magnetic sensor can be decoded to determine turn countinformation. This can be done with a half-turn resolution. Such outputscan be bridge voltage outputs from the multi-turn magnetic sensor. Theoutput voltages can represent three states: low, medium, and high. Thestate that each half-bridge inhabits can be determined by the magneticangle. Thresholds for these states can be determined by a giantmagnetoresistance (GMR) effect of the multi-turn magnetic sensor.

Based on the type of sensor initialization, the turn count informationcan be calculated by pairing successive half-bridges from a spiral ofthe multi-turn magnetic sensor and determining the transition from twohalf-bridges being low to either of the two half-bridges not being low.A successive approximation routine can determine the half-bridges ofinterest and calculate the turn count information. This can result in arelatively high speed turn count decoding with relatively low powerconsumption.

To decode a turn count for some multi-turn magnetic sensors using anexhaustive sequential readout technique, all half-bridge voltages fromthe multi-turn magnetic sensor are measured and re-ordered in the orderof the magnetic sequence, that is, the location of the half-bridge inthe magnetic spiral of the multi-turn sensor. This can involve aninteractive routing of comparing each half-bridge state to thesuccessive half-bridge state to determine the transition from bothbridges being low to either of them not being low. Such a method caninvolve N conversions and comparisons, in which N is the number ofhalf-bridges of the multi-turn magnetic sensor. As an example, for a 40turn magnetic sensor, the sequential readout technique can be more than5 times slower and also consume more power relative to successiveapproximation decoding techniques discussed herein.

Introduction to Magnetic Sensors

Magnetic sensors can be used to monitor the angular position and/orrotational velocity of a moving shaft. Such magnetic sensing can beapplied to a variety of different applications, such as automotiveapplications, medical applications, and industrial control applications,among others. Several technologies exist for making magnetic sensors.For instance, there are Hall-effect sensors. Hall-effect sensors cangenerate direct current output voltages based on the strength of anapplied magnetic field. A rotating magnetic field creates sinusoidalwaveforms in Hall-effect sensors which can then be processed by acomputer to calculate angle. There are also giant magnetoresistance(GMR) sensors. In a GMR sensor, GMR resistors are formed using layers offerromagnetic and non-magnetic materials laid out as a magnetoresistancetrack. The GMR resistors can be used in Wheatstone bridges to sensevariations in rotating magnetic fields.

Magnetic sensors can be integrated on a chip for sensing and recordingthe number of turns in half-turn increments, in which states can changeevery quarter turn, or for sensing the angle of a rotating magneticfield. A magnetic sensor for sensing and recording the number of turnsin increments can be interchangeably referred to as a multi-turn sensoror a multi-turn counter. Multi-turn sensors can count at variousresolutions, such as whole turns, half turns, quarter turns, etc., andthe multi-turn sensor can change its properties at various incrementsthat may be different than the count resolution. A magnetic sensor forsensing the rotational angle over a range of 360 degrees can be referredto as an angle sensor or as a single turn (360 degrees) angle sensor.

Both a multi-turn sensor and an angle sensor can be used together todetermine the rotational angle position that exceeds 360 degrees. Thiscombination of a multi-turn sensor with an angle sensor can also bereferred to as a multi-turn angle sensor. For instance, in automotiveapplications, multi-turn angle sensors can be used for drive-by-wiresystems. The angle sensor can detect the steering wheel angle, and amulti-turn sensor can track how many times a steering wheel has beenturned. This allows a vehicle control system to differentiate betweenwhen a steering wheel is at 45 degrees or 405 degrees, despite thesteering wheel being in the same position at both angles.

Additional circuitry can be used to process and/or convert signals fromthe multi-turn sensor and the angle sensor into position information.For instance, an analog-to-digital converter (ADC) can be used toconvert voltages from the sensors into digital data that can beprocessed to determine the overall rotational angle position and/orangular velocity. The accuracy of these conversions can depend upon manyfactors including sensor placement, environmental factors such astemperature, and magnetic field strength, to name a few.

The position information can represent rotations of a magnetic field.The magnetic field can be generated by a magnetic target, which caninclude one or more magnets. Such a magnetic target can be part of orattached to any suitable object, such as a shaft, gear, linear or rotaryactuator, a modular clutch actuator (MCA), steering wheel, etc. Theposition information can represent an angle or rotation, even rotationsof more than 360 degrees. Accordingly, the position information canrepresent an overall angle of rotation an object that includes or isattached to the magnetic target.

The multi-turn sensor can include magnetoresistive sensing elements. Forinstance, the multi-turn sensor can be a GMR sensor. The angle sensorcan include any suitable angle sensor, such as a Hall effect sensor, ananisotropic magnetoresistive (AMR) sensor, other magnetoresistivesensing elements, or the like. The angle sensor can provide an outputindicative of an angle in a range from 0 degrees to 360 degrees.

FIG. 1 is a schematic block diagram of a magnetic multi-turn anglesensor system 160 that includes a multi-turn sensor 100 and an anglesensor 166 according to an embodiment. The multi-turn angle sensorsystem 160 can also include a processing circuit 168 and a printedcircuit board (PCB) 163 on which the multi-turn sensor 100, the anglesensor 166, and the processing circuit 168 are disposed. The processingcircuit 168 can receive signal(s) S_(M) from the multi-turn sensor 100and signal(s) S_(A) from the angle sensor 166 and then process thesereceived signals to provide a rotational angle position Position. Theprocessing circuit 168 can include a half-turn decoder 169. Thehalf-turn decoder 169 can receive signal(s) S_(M) from the multi-turnsensor 100 and output a half-turn count. The half-turn decoder 169 canimplement successive approximation decoding and/or any suitableprinciples and advantages discussed herein related to decoding a turncount of the multi-turn sensor. The signal(s) S_(M) from the multi-turnsensor 100 and the signal(s) S_(A) from the angle sensor 166 can beanalog signals. For instance, the signal(s) S_(M) from the multi-turnsensor 100 can be voltage signals derived from resistor networks, suchas Wheatstone bridges including GMR resistors.

FIG. 2 shows an example magnetic strip layout representation of amulti-turn sensor 100 with a corresponding circuit schematicrepresentation 150. In the embodiment of FIG. 2, a magnetic strip ispatterned on a chip as a giant magnetoresistance track 101 that isphysically laid out in the shape of a spiral. The magnetoresistive track101 has corners 105 and segments 103 a to 103 n forming magnetoresistiveelements R1 to R14 arranged in series with each other, and a domain wallgenerator 107. The magnetoresistive elements can act as variableresistors that change resistances in response to a magnetic alignmentstate. The magnetoresistive track 101 of the multi-turn sensor 100illustrated can be implement in a multi-turn counter that can count atleast 3 turns. The magnetoresistive track 101 can have a magneticanisotropy, such as a high anisotropy, based on the material and crosssectional dimensions of the magnetoresistive track 101. Themagnetoresistive track 101 can store magnetic energy.

A domain wall generator (DWG) 107 is coupled to one end of themagnetoresistive track 101. The DWG 107 can have a magnetic anisotropy,such as a low anisotropy. The DWG 107 can be affected by a magneticfield. As the external magnetic field turns, the DWG 107 can injectdomain walls through the magnetoresistive track 101. The domain wall canpropagate through the segments, causing magnetic domain orientations ofthe segments to change. Each half turn of the magnetic field (up to amaximum number of half turns) will cause the domain walls to bepositioned such that the resistances of the segments 103 a to 103 n ofthe magnetoresistive track 101 to be in a unique sequence.

The segments 103 a to 103 n of the magnetoresistive track 101 are shownas straight sides of the magnetoresistive track 101 in the example ofFIG. 2. The segments 103 a to 103 n can have a variable resistance basedon the magnetic domain of each respective segment. As the orientation ofa magnetic domain of a segment changes, the resistance of that segmentcan change. Accordingly, the segments 103 a to 103 n can operate asmagnetoresistive elements, also referred to as variable resistors R1 toR14, respectively, herein. The magnetoresistive elements R1 to R14 canalso function as non-volatile, magnetic memory that can be magneticallywritten and electrically read. The magnetoresistive elements R1 to R14,as laid out in the spiral shaped magnetoresistive track 101, are coupledin series with each other. Corresponding circuit schematicrepresentation 150 shows segments 103 a to 103 n depicted ascorresponding magnetoresistive elements R1 to R14, respectively,connected in series.

A multi-turn sensor can provide various outputs that can be uniquelydecoded into a half-turn count. For instance, the multi-turn sensor 100can provide various half-bridge output signals, which can be voltages.The voltages can be measured at different locations, such as from thedifferent corners 105 of the multi-turn sensor. The measured voltagescan be stored by the half turn decoder 169 of FIG. 1. Then, the halfturn decoder 169 can, based on which corners have which voltages (and/oron the sequence of currents or resistances that correspond to thevoltages according to V=I*R), determine a number of half turns of themagnetic field that caused the sequence of resistances to appear. Insome embodiments, the number of half turns can be determined accordingto a routine or by referencing a pre-populated lookup table stored in amemory.

Decoding the Multi-Turn Sensor

With respect to FIG. 1 and FIG. 2, the multi-turn sensor 100 can be inthe shape of a spiral, and the signals S_(M) can provide the half turndecoder 169 a voltage reading across segments or corners of themulti-turn sensor 100.

A half turn decoder can sequentially receive voltage measurements at theends of the segments (e.g., the corners or opposite corners) such asshown in FIG. 2, from one end of the multi-turn sensor to the other.Then, based on the voltage readings for each segment, the half turndecoder can decode a number of half turns. Although examples in thisdisclosure may relate to half turns, any suitable principles andadvantages discussed herein can be applied to decoding a turn count withany suitable resolution for a particular application, such as a wholeturn, half turn, quarter turn, etc. Moreover, although examples in thisdisclosure involve voltage measurements, any other suitable signal canbe measured for a particular application, such as a current signal foran application that can decode a turn count using a current measurement.

Each voltage reading takes time and consumes power. When a relativelylong sequence of voltages is read, the amount of time and power used fordecoding the multi-turn sensor can become relatively large. Somerelatively large multi-turn sensors have long tracks for counting arelatively large numbers of turns. For relatively large multi-turnsensors, sequentially reading the voltages from one end of the largemulti-turn sensor to the other end consumes large amounts of power andtakes large amounts of time. Reading outputs in parallel may providefaster speeds at the cost of using significantly more chip area. Thisdoes not necessarily provide any power savings.

A faster, more energy efficient method can be used to decode themulti-turn sensor 100 using a successive approximation readout (SAR)technique. The half turn decoder 169 of FIG. 1 can implement the SARtechnique. Recognizing that the sequence of domain walls generated bythe movement of the DWG includes unique subsets for different halfturns, those unique subsets can be identified and the number of halfturns can be decoded without determining the orientations of all of thedomain walls (e.g., without determining the resistances of all of thesegments or without determining the voltages of all of the corners ofGMR spiral).

The signals S_(M) in FIG. 1 can include pairs of voltages taken fromdifferent parts of the multi-turn sensor 100. For example, the half turndecoder 169 can receive a first pair of voltages from a first pair ofcorners of the multi-turn sensor 100, and then the half turn decoder 169can receive a pair of voltages from a different pair of corners of themulti-turn sensor 100, and so on such that the half turn decoder 169iteratively receives a sequence of pairs of voltages. In each iteration,the half turn decoder 169 can be configured to read the voltages and usethe reading to determine which of the corners of the multi-turn sensorto read in the next iteration. The half turn count can be determined insubstantially less iterations according to the equation:HTC_(max)≤2^(i)  Equation 1

In Equation 1, HTC_(max) indicates a maximum number of half turn countsthat a multi-turn sensor 100 is configured to detect, and i indicatesthe number of iterations where i is the smallest positive integer thatsatisfies the equation. During each iteration, a value for a bit in abinary representation of a number of half turns can be decoded. Forexample, a magnetic sensor for detecting 0-127 half turns (or 64 turnsor 128 half turns) could be decoded in 7 iterations (2⁷=128). Notably,the integers from 0-127 can be represented as a 7-bit binary number. Insome embodiments, voltages can be read from up to two different nodesduring each iteration such that up to 2^(i) voltage readings areperformed to decode a half turn count. The iterative technique can beperformed substantially faster than reading voltages from each of thecorners of the corresponding 128 half-turn sensor and also performedusing less power. Significant benefits can be realized when decoding amulti-turn sensor for measuring 8 or more half turn counts.

Example Readout Structure

FIG. 3 shows a multi-turn magnetic sensor 300 with an example readoutstructure. The multi-turn magnetic sensor 300 includes a plurality ofmagnetoresistive elements (similar to R1 to R13 of FIG. 2 but notre-labeled in FIG. 3 for clarity) and a plurality of nodes N₀-N₁₅ atwhich voltages can be measured, detected, and/or read from as theoutputs of half Wheatstone bridges. Half Wheatstone bridges canalternatively be referred to as half-bridges. A voltage rail Vcc havinga first voltage is coupled to top left corners of each loop of thespiral. The bottom right corners of each loop of the spiral are coupledto a second voltage, such as ground (GND).

The multi-turn magnetic sensor 300 includes loops of rings. For example,a first loop can start at the innermost Vcc node and continue clockwiseuntil the next Vcc node is reached. The magnetoresistive segments ineach loop can be thought of as variable resistors in a Wheatstonebridge. Other embodiments can include differential voltage rails, suchas Vcc on a first voltage rail and a different voltage on the secondvoltage rail.

The voltages of the nodes N₀-N₁₅ can be measured in pairs. A voltage ata node can be measured and it can be determined whether the measurevoltage is within a voltage range. For example, a first “low” voltagecan be determined if the voltage is within a first range (such as below−50 mV), a second “medium” voltage can be determined if the voltage iswithin a second range (such as from −50 mV to 50 mV), and a third “high”voltage can be measured if the voltage is in a third range (such as 50mV or higher). In some embodiments, the SAR technique can includedetecting whether a voltage is within a voltage range (such as “high”)or not. Such embodiments may not involve distinguishing between othervoltages (such as “medium” and “low”).

In various embodiments, the voltage ranges can vary based on the valuesof the power rail(s) and/or the resistances of the segments of the GMRspiral. In some embodiments, the “low,” “medium,” and “high” ranges canbe different for nodes in different loops of the spiral. In variousembodiments, the spiral can include more loops and be configured todetect greater numbers of half turns. In various embodiments, the DWGcan be on either end of the multi-turn magnetic sensor 300.

A successive approximation readout technique can be used to sequentiallyread pairs of voltages and decode a binary number indicating a half turncount. In a first iteration, a readout of first measured voltages from afirst pair of nodes of a magnetoresistive track can be performed. Thefirst pair of nodes can be nodes toward a middle loop of the spiral ornodes that correspond to the number of bits used to indicate the halfturn count. The first, most significant bit of the half turn count canbe decoded based on the first measured voltages (e.g., whether thevoltages are both high, both low, or different values such as high andlow). The next pair of nodes to be read during the next iteration canalso be selected based on the measured voltages from the first pair ofnodes (e.g., whether they are both high, both low, or different values).Then, during the next iteration, the next pair of nodes can be read, andthe next bit of the half turn count can be decoded (e.g., whether theyare both high, both low, or different values such as high and low). Theiterations can continue until a sufficient number of nodes are read touniquely decode the half turn count.

In various embodiments, the successive readings can be changed based onwhich end (the interior or exterior end) of a GMR spiral the DWG islocated, whether clockwise or counter clockwise turns are being counted,the values of power rails such as Vcc and GND, and the like. A flowchartshowing an example of a successive approximation readout technique isshown in FIG. 5. A flowchart showing a more specific example of asuccessive approximation readout technique is shown in FIG. 6. Anexample showing signal levels at nodes of a GMR spiral is discussed withrespect to FIG. 7.

FIG. 4 shows an example decoder circuit 400 for reading pairs ofvoltages from the multi-turn sensor 300 of FIG. 3 and decoding the turncount of the multi-turn sensor 300. The decoder circuit 400 outputs ahalf-turn count HTC based on readings from the multi-turn sensor 300.The illustrated decoder circuit 400 includes a multiplexer (MUX) 401, anamplifier 403, an analog-to-digital converter (ADC) 405, a biascontroller 407, a decoder logic circuit and interface 409, andnon-volatile memory (NVM) 411.

From the multi-turn sensor 300, each of the nodes (such as nodes N₀-N₁₅shown in FIG. 3) is electrically coupled to a different input of themultiplexer 401. The multiplexer 401 is configured to select one of thenodes of the multi-turn sensor 300 to be electrically coupled throughthe output of the multiplexer 401 to the amplifier 403. In someembodiments, the amplifier 403 can be a programmable gain amplifier(PGA). Accordingly, a voltage from one of the nodes of the multi-turnsensor 300 is selected to be provided to the input of the amplifier 403.

The amplifier 403 is configured to amplify the voltage received at theamplifier input and to generate an amplified signal at the output of theamplifier 403. The amplified signal is provided to the input of the ADC405. The amplifier 403 can be biased using a bias network 407. In someembodiments, the ADC 405 can be a 1 bit ADC, such as a comparator, andthe bias network 407 can provide a reference voltage to be comparedagainst.

The output of the ADC 405 can be a digital output signal that indicatesa measurement or range of the voltage received at the input of the ADC405. The ADC 405 can output different values for the digital outputsignal to distinguish between receiving low, medium, or high voltages.For example, the ADC can output b'01 (in which b'01 denotes bits 01) inresponse to detecting a low voltage (such as below −50 mV or withinother thresholds), output b'10 in response to detecting a medium voltage(such as from −50 mV to 50 mV or within other thresholds), and outputb'11 in response to detecting a high voltage (such as 50 mV or higher orwithin other thresholds). In some embodiments that include a comparatorfor the ADC 405, the output of the ADC 405 can indicate whether thevoltage at the input of the ADC 405 is greater than or lower than areference voltage provided by the bias circuit 407. Accordingly, the ADC405 is configured to detect or measure the voltage from a selected nodeof the multi-turn sensor 300 and generate a digital output signal basedat least in part on the voltage of the selected node of the multi-turnsensor 300. In some embodiments, different voltage thresholds can beused for different resistive segments of the multi-turn sensor 300. Thedifferent voltage thresholds can account for the different lengths ofthe resistive segments. For example, as shown in FIG. 2, resistor R13 islonger than R1. Additionally or alternatively, a different gain can beapplied to the amplifier 403 to calibrate for the variations in theresistances of different segments.

The decoder logic circuit and interface 409 can receive and decode thedigital output signals. For example, this can involve decoding accordingto any suitable features discussed with references to the flowchartsshown in FIG. 5 and FIG. 6, respectively. In some embodiments, thedecoder logic circuit and interface 409 can include a statement machineimplementation of features discussed with reference to the flowcharts ofFIGS. 5 and/or 6 and/or a digital processor programmed to implementfeatures discussed with reference the flowcharts of FIGS. 5 and/or 6.The decoder logic circuit and interface 409 can include a communicationsinterface such as a serial peripheral interface (SPI) or other suitableinterface to output a detected turn count, such as a half turn count(HTC).

The decoder logic circuit can also include logic to set the value forthe control signal provided to the multiplexer 401. The control signalcan be set to sequentially select the nodes of the multi-turn sensor 300for voltage detection according to a successive approximation readouttechnique. For example, the control signal can be configured to selectthe nodes as indicated in block 505 of FIG. 5 and/or block 609 of FIG.6. Accordingly, a sequence of nodes can be selected to quickly andefficiently decode the turn count of the multi-turn sensor 300.

A non-volatile memory (NVM) 411 can be used to store calibration valuesfor other components of the decoder circuit 400, such as a gain for theamplifier 403 and/or coefficients for calibrating an offset of each halfbridge output voltage from various nodes of the multi-turn sensor 300.Calibration coefficients can include gains for applying to the amplifier403 and/or different threshold voltages to be used for differentresistor segments. In some embodiments, the NVM 411 can store a lookuptable for referencing to decode a half turn count according to measuredvoltages. In some embodiments, the NVM 411 can store an indication ofthe voltage value as the voltages are read from different nodes. When asuccessive approximation readout depends on a voltage value of a nodethat has been read during the same decoding process and is stored in theNVM 411, the stored voltages can be read from the NVM 411 instead ofre-reading the voltage from the node on the multi-turn sensor 300.

Various embodiments of the decoder circuit 400 can include more or fewerelements. For example, a parallel path can be added to select and readvoltages from two or more nodes of the multi-turn sensor 300 at a time.This can include a first multiplexer and processing path for reading oddnodes and a second multiplexer and processing path for reading evennodes in parallel. In some embodiments, the amplifier or ADC can beomitted.

Successive Approximation Readout Technique

FIG. 5 shows a flow diagram of an example process 500 for decoding halfturns from outputs of a multi-turn sensor using a successiveapproximation readout technique. The process 500 can be implemented byany suitable electronic circuitry configured to determine a half-turncount (HTC) from a multi-turn sensor output, such as the multi-turnsensor 300 shown in FIG. 3. The HTC can be decoded into a binary number.The successive approximation readout method can be implemented in avariety of different ways for a variety of multi-turn sensors. Forexample, voltages may be detected as high or low, numbers can be addedor subtracted, numbers can be initialized differently, etc. based onwhich end of a spiral the DWG is located, based on whether clockwise orcounterclockwise turns are considered as “positive” turns, based on aninitialized state of the magnetoresistive elements, based on how thenodes are numbered, and based on other factors. A specific example of animplementation of the example process 500 is discussed with respect toFIG. 6.

At block 503, an initial iterator (i) can be set, and an node number “n”(e.g., N_(n)) of the multi-turn sensor can be selected. The iterator canbe set to a number of iterations sufficient to determine the HTC using asuccessive approximation readout technique. The iterator can be set toan integer indicating a number of bits sufficient to represent a maximumHTC in binary. For example, if the decoder is configured to count 0 to63 half turns as a binary number using bits [5:0], then the iterator canbe set to the number of bits that can represent a full turn count orequivalently one less than the number of bits that can represent thehalf turn count. For example, the iterator can be set to 5 or 6. Invarious embodiments, the iterator can count up or down. For example, theiterator can start at 0 and count up. The iterator can be initialized toany number useful for tracking a number of iterations.

The node number n is selected to have a voltage measured and/ordetected. For example, with respect to FIGS. 3 and 4, a node N₈ (n=8)can be selected by setting an appropriate value for the control signalprovided to the multiplexer 401. An initial value for n can be selectedas any of the nodes. In certain embodiments, n can be selected to be anumber that is approximately the value of the most significant bit ofthe HTC, such as the value of the MSB+/−1. For example, if the maximumHTC is decimal 30, then the HTC can be represented with a five bitbinary number [4:0] because 2⁵=32, which is greater than 30. Because2^(MSB)=2⁴=16, the node N₁₆ (n=16) can be selected as the initial node.In some other embodiments, the node can be selected to be about half ofthe maximum possible HTC according to the numbering scheme shown in FIG.3.

At block 505, the output from node number n can be read. The output canbe a half bridge voltage output or Wheatstone bridge voltage output. Thevoltage measurement can be read using a voltmeter, analog to digitalconverter, comparator, or other indicator of voltage.

At block 506, the output from node n±1 according to the numbering schemeof nodes shown in FIG. 3 can be read. For example, if the output fromnode N₈ of FIG. 3 was read at block 505, then the output from node N₇ ofFIG. 3 can also be read at block 506. Whether 1 is added to orsubtracted from n can depend on the initially selected node (e.g., if N₇is selected at block 505), how the nodes are numbered, and other similarconsiderations. The outputs can be a voltage measurement that is readusing a voltmeter, analog-to-digital converter, comparator, or otherindicator of voltage.

At block 507, a successive bit of the HTC can be determined based on theoutputs of node n and node n±1 that were read at block 505 and block506. For the first iteration of “i,” the successive bit can be the mostsignificant bit of the HTC. In successive iterations, the successive bitcan be the next most significant bit of the HTC. In some embodiments,the successive bit can be set to 1 if both of the voltage outputs ofnode n and node n±1 are low, otherwise the successive bit can be set to0. The successive bit of the HTC can be set to 1 or 0 depending onwhether or not both the nodes n and n±1 are low or high. The particularimplementation can depend on the setup, such as the connections of thepower rails and/or other factors. In some instances, a full readout ofall voltages of all nodes for all half turns can be measured, and thedecision at block 507 can be based on which voltage readouts of certainnode pairs are unique to which specific HTC counts.

At block 509, it can be determined if the iterations are complete. Ifthe number of iterations sufficient to decode all bits of the HTC hasbeen completed, then block 509 can proceed to block 511. At block 511,the decoded turn count of the multi-turn sensor can be output.Otherwise, block 509 can proceed to block 513.

At block 513, the iterator can be incremented. For example, the iteratorcan be added to or subtracted from, depending on whether the iterator iscounting up or down.

At block 515, a next node number “n” is selected. The number “n” can beselected based at least in part on the output of node n and the outputof node n±1 from block 507 of the latest iteration. Because the outputsof node n and n±1 can be used at block 507 to set the currentlyapproximated value of the HTC, the next node number “n” can also beselected based on the current HTC approximation. In some embodiments,the next node number n can be changed by adding or subtracting a valueof a next most significant bit. For example, if n is presently equal to16, then N+8 (which is 24) or N−8 (which is 8) can be selected as thenode number, depending on the values of the voltage outputs of N_(n) andN_(n±1) detected at blocks 505 and 506. In some embodiments, the nextnode number n can be selected to be about halfway between the presentvalue of n and the maximum HTC or about halfway between the presentvalue of N and the minimum HTC, depending on the values of the voltageoutputs of N_(n) and N_(n±1) detected at blocks 505 and 506. Whether thenumber n is increased or decreased can depend on the setup. In the eventthat a next value for n falls outside of a valid range of nodes, thenthe changes to the HTC can be disregarded for the next iteration, Afterthe node number n is selected at block 515, the next iteration of block505 can proceed.

Successive Approximation Readout Examples

FIG. 6 shows a flow diagram of an example process 600 for decoding halfturns of a multi-turn sensor using a successive approximation readouttechnique. The process 600 can be implemented by any suitable electroniccircuitry configured to determine a half-turn count (HTC) from anexample multi-turn sensor output. The process 600 is discussed withrespect to an example multi-turn sensor that can count 40 full turns andis configured to determine a HTC from 0 to 79. The HTC can be decodedinto a binary number with bits [6:0]. The example multi-turn sensorincludes a DWG located on the outside of the spiral, and the multi-turnsensor can be configured to count counterclockwise turns for “positive”turns of a magnetic target. The nodes are numbered from 0 to 79, withnode 0 starting at the exterior loop of the spiral.

At block 603, an initial iterator (i) can be set to 6, and the HTC canbe initialized to zero. The maximum HTC is 79, which can be representedby a 7 bit number (1001111), in this example. Bit 6 of the HTC thatincludes bits [6:0] is the most significant bit, and bit 0 of the HTC isthe least significant bit. The iterator i can be initialized to 6, whichis the position of the most significant bit.

At block 605, the HTC is changed by adding 2^(i) to the previous valueof HTC. For the first iteration, the initial HTC of 0 is changed byadding 2⁶ to 0, which equals 64, such that the HTC is set to 64.

At block 607, n is set to the value of the HTC. For the first iteration,n is set to the value of the HTC determined in block 605 such that nodeN₆₄ according to the numbering scheme shown in FIG. 3 applied to aspiral with more turns is selected. For subsequent iterations (e.g.,other than the first iteration), n can be set to the value of theupdated value of HTC as determined in blocks 611 or 613. Accordingly,for subsequent iterations (e.g., other than the first iteration) thevalue of n as set in block 607 depends, at least in part, on a previousmeasurement of the multi-turn sensor measured at block 609.

At block 609, the half bridge voltage outputs from node n and from noden−1 according to the numbering scheme shown in FIG. 3 applied to aspiral with more turns can be read. If the half bridge voltage outputsfrom node n and from node n−1 are both low, then block 609 proceeds toblock 611, otherwise block 609 proceeds to block 613. In the process600, a decision at block 609 and the subsequent computation at eitherblock 611 or block 613 can determine each bit of the HTC.

At block 611, the HTC is changed by subtracting 2^(i) from the previousvalue of HTC, effectively undoing the change at block 605. For the firstiteration, if block 611 is performed, value of HTC would be set to64−2⁶, which equals 0, such that the most significant bit of the HTC isset to 0.

At block 613, the HTC remains unchanged. For the first iteration, ifblock 613 is performed, the most significant bit of the HTC remains setas 1. It is recognized that in some embodiments, a mathematicallyequivalent process can be performed without block 605 if block 609 ischanged to “HTC=HTC+2^(i),” block 611 is changed to “HTC=HTC,” and block607 indicates that N is set to HTC+2^(i).

At block 615, it can be determined if the iterator indicates that theHTC has been fully decoded, which occurs when the iterator is equal tozero in the process 600. If so, then block 615 can proceed to output thedecoded half turn count at block 617. Otherwise, block 615 can proceedto block 619.

At block 619, the iterator can be decremented by 1, thus beginning thenext iteration. Block 619 can then proceed to block 605 such that blocks605-615 are performed again to determine a next successive bit of theHTC.

FIG. 7 shows example voltage outputs from various nodes of a multi-turnsensor. FIG. 7 is based on an example multi-turn sensor for counting 0to 15 half turns, such as sensor 300 shown in FIG. 3. Half bridgevoltage outputs are shown for each node N₀-N₁₅ of FIG. 3. Nodes N₀-N₇are shown in a first column, and nodes N₉-N₁₅ are shown in a secondcolumn. At the bottom of each column, an axis indicates a turn anglefrom 2250 degrees to 2520 degrees. For reference, 2340°/180°=13 halfturns. Each of the voltage outputs for the nodes N₀-N₁₅ are shown as alow, medium, or high voltage across the corresponding range of turnangles indicated by the axis. It will be understood that the nodesN₀-N₁₅ can have other voltage outputs outside of the illustrated rangeof turn angles. Unless indicated as binary, all numbers are in decimalformat. To provide additional clarity, some decimal numbers may bespecifically indicated as decimal using the “dec” suffix and binarynumbers are preceded by “b”.

As a first example, the process shown in FIG. 6 can be used to decodethe voltage outputs to determine a half turn count in four iterationswhen the magnetic target has been turned to 2300 degrees. Accordingly,for each node, the voltage values of low, medium, or high can be readalong an axis section between 2250 and 2340. The HTC can be decoded intoa four bit number represented by bits [3:0]. Accordingly, at block 603,i can be initialized to 3, and the HTC is set to b'0000=0dec.

In a first iteration (i=3), at block 605, HTC is set to 0+2³ such thatthe HTC=b'1000=8dec. At block 607, node number n=HTC is selected so thatn=8. At block 609, the half bridge voltage outputs of nodes N₈ and N₇ ofthe multi-turn sensor 300 of FIG. 3 are read. According to the outputgraphs, the voltage output for node N₈ is low and the voltage output fornode N₇ is high. Accordingly, the decision in block 609 is false, andblock 609 proceeds to block 613, where the HTC remains unchanged. Atblock 615, the iterations are not complete, and at block 619, theiterator i decrements by 1 such that i=2.

In a second iteration (i=2), at block 605, HTC is set to 8+2² such thatthe HTC=b'1100=12dec. At block 607, node number n=HTC is selected sothat n=12. At block 609, the half bridge voltage outputs of nodes N₁₂and N₁₁ of the multi-turn sensor 300 of FIG. 3 are read. According tothe output graphs, the voltage output for node N₁₂ is low and thevoltage output for node N₁₁ is high. Accordingly, the decision in block609 is false, and block 609 proceeds to block 613, where the HTC remainsunchanged. At block 615, the iterations are not complete, and at block619, the iterator i decrements by 1 such that i=1.

In a third iteration (i=1), at block 605, HTC is set to 12+2¹ such thatthe HTC=b'1110=14dec. At block 607, node number n=HTC is selected sothat n=14. At block 609, the half bridge voltage outputs of nodes N₁₄and N₁₃ of the multi-turn sensor 300 of FIG. 3 are read. According tothe output graphs, the voltage output for node N₁₄ is low and thevoltage output for node N₁₃ is low. Accordingly, the decision in block609 is true, and block 609 proceeds to block 611, where the HTC is setto 14-2¹ such that the HTC=b'1100=12dec. At block 615, the iterationsare not complete, and at block 619, the iterator i decrements by 1 suchthat i=0.

In a fourth iteration (i=0), at block 605, HTC is set to 12+2⁰ such thatthe HTC=b'1101=13dec. At block 607, node number n=HTC is selected sothat n=13. At block 609, the half bridge voltage outputs of nodes N₁₃and N₁₂ of the multi-turn sensor 300 of FIG. 3 are read. According tothe output graphs, the voltage output for node N₁₃ is low and thevoltage output for node N₁₂ is low. Accordingly, the decision in block609 is true, and block 609 proceeds to block 611, where the HTC is setto 13-2⁰ such that the HTC=b'1100=12dec. At block 615, the iterationsare complete, and the HTC is decoded as 12 half turns, which correspondsto 2300° as 2300° is more than 12 half turns (2160°) and less than 13half turns (2340°). The half turn count is output at block 617.

In some embodiments, the voltage for N₁₃ can be stored in a memory (suchas the NVM 411 of FIG. 4) during the third iteration. As part of thefourth iteration, the voltage for N₁₃ can be read from the memoryinstead of re-measuring the voltage from the node on the multi-turnsensor. This can result in reduced power consumption and/or reduced timeto decode a half turn count in certain instances.

As a second example, the process shown in FIG. 6 can be used to decodethe voltage outputs to determine a half turn count in four iterationswhen the magnet target has been turned to 2400 degrees, whichcorresponds to a half turn count of 13. Accordingly, for each node, thevoltage values of low, medium, or high can be read along an axis sectionbetween 2340 and 2430. The HTC can be decoded into a four bit numberrepresented with bits [3:0]. Accordingly, at block 603, i can beinitialized to 3, and the HTC is set to b'0000=0dec.

In a first iteration (i=3), at block 605, HTC is set to 0+2³ such thatthe HTC=b'1000=8dec. At block 607, node number n=HTC is selected so thatn=8. At block 609, the half bridge voltage outputs of nodes N₈ and N₇ ofthe multi-turn sensor 300 of FIG. 3 are read. According to the outputgraphs, the voltage output for node N₈ is low and the voltage output fornode N₇ is high. Accordingly, the decision in block 609 is false, andblock 609 proceeds to block 613, where the HTC remains unchanged. Atblock 615, the iterations are not complete, and at block 619, theiterator i decrements by 1 such that i=2.

In a second iteration (i=2), at block 605, HTC is set to 8+2² such thatthe HTC=b'1100=12dec. At block 607, node number n=HTC is selected sothat n=12. At block 609, the half bridge voltage outputs of nodes N₁₂and N₁₁ of the multi-turn sensor 300 of FIG. 3 are read. According tothe output graphs, the voltage output for node N₁₂ is low and thevoltage output for node N₁₁ is high. Accordingly, the decision in block609 is false, and block 609 proceeds to block 613, where the HTC remainsunchanged. At block 615, the iterations are not complete, and at block619, the iterator i decrements by 1 such that i=1.

In a third iteration (i=1), at block 605, HTC is set to 12+2¹ such thatthe HTC=b'1110=14dec. At block 607, node number n=HTC is selected sothat n=14. At block 609, the half bridge voltage outputs of nodes N₁₄and N₁₃ of the multi-turn sensor 300 of FIG. 3 are read. According tothe output graphs, the voltage output for node N₁₄ is low and thevoltage output for node N₁₃ is low. Accordingly, the decision in block609 is true, and block 609 proceeds to block 611, where the HTC is setto 14-2¹ such that the HTC=b'1100=12dec. At block 615, the iterationsare not complete, and at block 619, the iterator i decrements by 1 suchthat i=0.

In a fourth iteration (i=0), at block 605, HTC is set to 12+2⁰ such thatthe HTC=b'1101=13dec. At block 607, node number n=HTC is selected sothat n=13. At block 609, the half bridge voltage outputs of nodes N₁₃and N₁₂ of the multi-turn sensor 300 of FIG. 3 are read. According tothe output graphs, the voltage output for node N₁₃ is low and thevoltage output for node N₁₂ is medium. Accordingly, the decision inblock 609 is false, and block 609 proceeds to block 613, and the HTCremains unchanged. At block 615, the iterations are complete, and theHTC is decoded as 13 half turns. This half turn count is output at block617.

As illustrated by the two examples discussed above with reference toFIG. 7, the HTC can be decoded after reading voltage outputs from 7different nodes, despite the multi-turn sensor having 16 differentnodes. Accordingly, the readouts can be more than twice as fast andconsume less than half of the power in comparison to reading the voltageoutputs from all of the nodes.

Example Magnetic Angle Sensor Systems

FIG. 8A is a schematic block diagram of a magnetic angle sensor system800 that includes a multi-turn sensor 100, an angle sensor 166, and aprocessor 168 a according to an embodiment. As illustrated, theprocessor 168 a includes an analog-to-digital converter (ADC) 802, anADC 804, a microcontroller 806, and a microprocessor 808. In theembodiment of FIG. 8A, the processor 168 a receives signals S_(M) fromthe multi-turn sensor 100 and signals S_(A) from the angle sensor 166.The signals S_(M) and S_(A) can be analog signals such as voltagesignals from Wheatstone bridges. The signals S_(M) from the multi-turnsensor 100 can be converted to digital signals S₁ by the ADC 802, andthe signals S_(A) from the angle sensor 166 can be converted to digitalsignals S₂ by the ADC 804. The ADC 804 provides the digital signals S₂to the microcontroller 806, which in turn can convert and process thisinformation. The microprocessor 808 can combine both the angle outputdata S₂ from the ADC 804 and the digital signals S₁ from the ADC 802 tocalculate the overall rotation angle position data Position. Themicrocontroller 806 can decode the output of the multi-turn sensor 100to determine a half-turn count. The microcontroller 806 can include adecoder arranged to decode a turn count of the multi-turn sensor inaccordance with any suitable principles and advantages discussed herein.For example, the microcontroller 806 can include a half-turn decoderconfigured to read and decode pairs of signals S_(M) from the multi-turnsensor 100 as disclosed herein. In some embodiments, the ADC 802 can beconfigured to detect whether a voltage is “low” or “high” in accordancewith the SAR technique. Accordingly, in some embodiments, the ADC 802can be implemented as a 1 bit voltage threshold detector or comparator.

FIG. 8B is a schematic block diagram of a magnetic angle sensor system840 including the multi-turn sensor 100, the angle sensor 166, and aprocessor 168 b according to another embodiment. The processor 168 b issimilar to the processor 168 a of FIG. 8A except it includes amicrocontroller 814. The microcontroller 814 can implement any suitableprinciples and advantages of the processing circuit 168 of FIG. 1.

FIG. 8C is a schematic block diagram of a magnetic angle sensor system850 including the multi-turn sensor 100, the angle sensor 166, and aprocessor 168 c according to an embodiment. The processor 168 c issimilar to the processors 168 a and 168 b except that the process 168 cincludes an ASIC 820 to processes outputs of the multi-turn sensor 100and the angle sensor 166. The ASIC 820 can implement any suitableprinciples and advantages of the processing circuit 168 of FIG. 1. TheASIC 820 can compute the overall rotation angle position data Position.In the embodiment of FIG. 8C, ASIC 820 can be configured to read anddecode pairs of signals S_(M) from the multi-turn sensor 100 asdisclosed herein. For example, the ASIC 820 can be a state machineimplementation or digital logic implementation of the processes of FIG.5 or FIG. 6. Although not every component is re-drawn, it will beunderstood that the systems of FIG. 8A, FIG. 8B, and FIG. 8C can includevarious implementations of the system 400 of FIG. 4.

Any of the principles and advantages discussed herein can be applied toother systems, not just to the systems described above. Some embodimentscan include a subset of features and/or advantages set forth herein. Theelements and operations of the various embodiments described above canbe combined to provide further embodiments. The acts of the methodsdiscussed herein can be performed in any order as appropriate. Moreover,the acts of the methods discussed herein can be performed serially or inparallel, as appropriate. While circuits are illustrated in particulararrangements, other equivalent arrangements are possible.

Any of the principles and advantages discussed herein can be implementedin connection with any other systems, apparatus, or methods that benefitcould from any of the teachings herein. For instance, any of theprinciples and advantages discussed herein can be implemented inconnection with any devices with a need for decoding a turn count of amulti-turn magnetic sensor.

Aspects of this disclosure can be implemented in various electronicdevices, components and/or systems related to multi-turn sensing. Forinstance, decoding methods and decoder circuits implemented inaccordance with any of the principles and advantages discussed hereincan be included in various electronic systems, devices, and/orelectronic components. For instance, aspects of this disclosure can beimplemented in any electronic system, electronic device, and/orelectronic component that could benefit from the technology disclosedherein. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products, electronic test equipment, vehicular electronicssystems, etc. Examples of the electronic devices can include, but arenot limited to, computing devices, communications devices, electronichousehold appliances, automotive electronics systems, other vehicularelectronics systems, industrial control electronics systems, medicalsystems or devices, etc. Further, the electronic devices can includeunfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including,” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The words “coupled” or“connected”, as generally used herein, refer to two or more elementsthat may be either directly connected, or connected by way of one ormore intermediate elements. Thus, although the various schematics shownin the figures depict example arrangements of elements and components,additional intervening elements, devices, features, or components may bepresent in an actual embodiment (assuming that the functionality of thedepicted circuits is not adversely affected). The words “based on” asused herein are generally intended to encompass being “based solely on”and being “based at least partly on.” Additionally, the words “herein,”“above,” “below,” and words of similar import, when used in thisapplication, shall refer to this application as a whole and not to anyparticular portions of this application. Where the context permits,words in the Detailed Description of Certain Embodiments using thesingular or plural number may also include the plural or singularnumber, respectively. The words “or” in reference to a list of two ormore items, is intended to cover all of the following interpretations ofthe word: any of the items in the list, all of the items in the list,and any combination of the items in the list. All numerical values ordistances provided herein are intended to include similar values withina measurement error.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, systems, andmethods described herein may be embodied in a variety of other forms.Furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

What is claimed is:
 1. A system for decoding a turn count of amulti-turn magnetic sensor, the system comprising: a multi-turn magneticsensor comprising a magnetoresistive track, the multi-turn magneticsensor configured to store a turn count; and a decoder circuit coupledto the magnetoresistive track, the decoder circuit comprising circuitryconfigured to couple to nodes of the magnetoresistive track, measuresignals associated with voltages of at least some of the nodes using asuccessive approximation readout technique, and determine the turn countbased at least in part on the measured signals; wherein the successiveapproximation readout technique comprises measuring signals associatedwith voltages of first nodes of the nodes, selecting a next node basedat least in part on the signals associated with voltages of the firstnodes, and measuring a signal associated with a voltage of the nextnode.
 2. The system of claim 1, wherein the next node is selected basedat least in part on whether the signals associated with the voltages ofthe first nodes each represent a voltage within a predefined range. 3.The system of claim 1, wherein the first nodes are associated withhalf-bridge circuits of the multi-turn magnetic sensor.
 4. The system ofclaim 1, wherein the decoder circuit is configured to determine a mostsignificant bit of the turn count in a first iteration of the successiveapproximation readout technique to determine the most significant bit ofthe turn count prior to determining other bits of the turn count.
 5. Thesystem of claim 1, wherein each bit of the turn count is determinedbased at least partly on a respective iteration of the successiveapproximation readout technique.
 6. The system of claim 1, wherein theturn count is a quarter turn count.
 7. The system of claim 1, whereinthe turn count is a half turn count.
 8. The system of claim 1, whereinthe multi-turn magnetic sensor is configurable into a state representing40 full turns.
 9. The system of claim 1, wherein the decoder circuitcomprises: a multiplexer configured to select a node from among thenodes of the magnetoresistive track; an analog-to-digital converterhaving an input coupled to an output of the multiplexer; and a decoderlogic circuit having an input coupled to an output of theanalog-to-digital converter, the decoder logic configured to determinethe turn count.
 10. The system of claim 1, further comprising an anglesensor, wherein the decoder circuit is included in a processing circuit,and wherein the processing circuit is configured to generate positiondata based at least in part on the turn count and an output of the anglesensor.
 11. The system of claim 1, wherein the multi-turn magneticsensor comprises a domain wall generator coupled to the magnetoresistivetrack.
 12. The system of claim 1, wherein the magnetoresistive track islaid out in a shape of a spiral, and the nodes are at corners of thespiral.
 13. A method of decoding a turn count of a multi-turn magneticsensor that comprises a magnetoresistive track, the method comprising:measuring signals associated with voltages of first nodes of themagnetoresistive track; selecting a next node of the magnetoresistivetrack based at least in part on the signals associated with the voltagesof the first nodes; measuring a signal associated with a voltage of nextnode of the magnetoresistive track; and decoding a turn count of themulti-turn magnetic sensor based at the signals associated with thevoltages of with the first nodes least and the signal associated withthe voltage of the next node.
 14. The method of claim 13, wherein thenext node is selected based at least in part on whether the signalsassociated with the voltages of the first nodes each represent a voltagewithin a predefined range.
 15. The method of claim 13, wherein thedecoding comprises determining a most significant bit of the turn countprior to determining other bits of the turn count.
 16. The method ofclaim 13, wherein the turn count is a quarter turn count.
 17. The methodof claim 13, further comprising: determining an angle using an anglesensor; and generating position data based on the angle and the turncount.
 18. A system for decoding a turn count of a multi-turn magneticsensor, the system comprising: a multi-turn magnetic sensor comprising amagnetoresistive track, the multi-turn magnetic sensor configured tostore a turn count; and means for decoding the turn count of themulti-turn magnetic sensor using a successive approximation readouttechnique; wherein the successive approximation readout techniquecomprises measuring signals associated with voltages of first nodes ofthe nodes, selecting a next node based at least in part on the signalsassociated with voltages of the first nodes, and measuring a signalassociated with a voltage of the next node.
 19. The system of claim 18,wherein the turn count is a quarter turn count.
 20. The system of claim18, further comprising an angle sensor, wherein the means for decodingis included in a processing circuit, and wherein the processing circuitis configured to generate position data based at least in part on theturn count and an output of the angle sensor.